The fluorosulfur containing pincer ligands 1,3-(CH 2 SR f ) 2 C 6 H 4 [R f = C 6 F 5 (1) and 4-HC 6 F 4 (2)] and 1,2,4,5-(CH 2 SR f ) 4 C 6 H 2 [R f = C 6 F 5 (3) and 4-HC 6 F 4 (4)] have been prepared by treatment of 1,3-(CH 2 Br) 2 C 6 H 4 or 1,2,4,5-(CH 2 Br) 4 C 6 H 2 with the corresponding lead thiolate Pb(SR f ) 2 .
Two different counter-ion-free host-guest complexes have been prepared and isolated. These compounds were formed from two equally and opposite doubly-charged species, the viologen guests 1 a(2+) and 1 b(2+) and the anti-disulfodibenzo[24]crown-8 [DSDB24C8](2-) host, which gave rise to the 1:1 neutral complexes [1 a⋅DSDB24C8] and [1 b⋅DSDB24C8]. These species are held together by hydrogen bonding and π stacking, as well as strong electrostatic interactions. The investigation of these neutral ion-paired supramolecular systems in solution and in the solid state allowed us to establish their co-conformational preferences. Compound [1 a⋅DSDB24C8], with small methyl groups as substituents on the viologen unit, may adopt three different geometries, 1) an exo nonthreaded, 2) a partially threaded, and 3) a threaded arrangement, depending on the relative spatial orientation between the host and guest: The partially-threaded structure is preferred in solution and in the solid state. The presence of bulky tert-butylbenzyl groups in the viologen moiety in compound [1 b⋅DSDB24C8] restricts the possible geometrical arrangements to one: The exo nonthreaded arrangement. This structure was confirmed in the solid state by X-ray crystallography. The stability of the neutral complexes in solution was determined by UV/Vis spectrophotometry. The stoichiometry of the complexes was established by continuous variation experiments, and overall equilibrium constants and ΔG° values were determined on the basis of dilution experiments. The results observed are a consequence of only the intrinsic stability of the complexes as there are no additional contributions from counter ions.
The use of the electrostatic stoppersc oncept in the fieldo fm echanically interlocked molecules is reported;t hese stoppers are chemically sensitive end groupso n al inear guest molecule that allows for the conversion of a pseudo-rotaxane speciesi nto ar otaxanec omplex by a changei nt he medium acidity.T he chemicals timulus causes the appearanceo fn egative chargeso nb oth ends of the linear component, passing from cationic to anionic, and causing as ignificant ring-to-axle electrostatic repulsion. This phenomenon has two different and simultaneous effects:1 )destabilizes the complexa saconsequence of confining an anionic ring into an anionic axle, and 2) increasest he dissociatione nergyb arrier, thus impeding ring extrusion. This newly formed metastable rotaxane species is resistant to solventa nd temperature effects and performs as at wo-state degenerated molecular shuttle in solution.
Platinum(ii) derivatives of the tridentate ligand Ph2PCH2CH2P(Ph)CH2CH2PPh2 (triphos), including [Pt(SRF)(triphos)](CF3SO3) RF = C6F4CF3-4 1, C6F52, C6HF4-4 3, C6H4CF3-4 4, C6H3F2-2,4 5, C6H4F-2 6, C6H4F-4 7 and C6H58, have been prepared and characterised.
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